Non-luminance lighting panel

ABSTRACT

A transparent prismatic low luminescent lighting panel of a type having a plurality of refracting prismatic elements on its outer surface in the form of pyramids or cones, said elements having curved surfaces, wherein said elements in conical form have cross-sectional profiles and are situated on the surface of the exterior face of said panel such that luminous rays which by reason of their angle of incidence relative to the panel, suffer little energy loss on travelling through the thickness of the panel and which because of incidence at certain points of the panel, emerge from said conical elements defining angles of between 60* and 90* with respect to the axis of symmetry of said conical elements strike an adjacent cone and suffer total internal reflection, thus reducing the low luminance of said panel. Said refracting elements of pyramidal form are situated on the exterior face of the panel forming therebetween narrow, flat zones which improve the light efficiency of said panel without having an unfavorable effect on the luminescence of said panel.

Q U' D I 9 United States Patent 1 1 Feb. 26, 1974 Taltavull 1 NON-LUMINANC IEJ LIGHTING PANEL [76] Inventor: Ignacio Goytisolo Taltavull, 83

Madrazo, Barcelona, Spain [22] Filed: Apr. 20, 1972 [2]] Appl. No.: 245,904

[52] US. Cl 240/106 R, 161/1, 350/167 [51] Int. Cl. F2lv 5/00 [58] Field of Search 240/106, 92; 350/109, 167; 161/1, 3.5

[56] References Cited UNITED STATES PATENTS 3,671,101 6/1972 Finch 350/109 3,038,065 6/1962 Frank ct a1 l 240/106 R 1,241,886 10/1917 Rowe 240/106 R 3,566,102 2/1971 Choyke,-Jr..... 240/106 R X 3,234,376 2/1966 Ceglia 240/106 R 3,578,967 5/1971 Stahlhut et a1. 240/106 R 3,096,032 7/1963 Davis 240/106 R 2,859,334 11/1958 Guth 240/106 R 2,474,317 6/1949 McPhail 240/106 R Primary Examiner.1oseph F. Peters, Jr. Attorney, Agent, or Firm-Wenderoth, Lind & Ponack [5 7] ABSTRACT A transparent prismatic low luminescent lighting panel of a type having a plurality of refracting prismatic elements on its outer surface in the form of pyramids or cones, said elements having curved surfaces, wherein said elements in conical form have cross-sectional profiles and are situated on the surface of the exterior face of said panel such that luminous rays which by reason of their angle of incidence relative to the panel, suffer little energy loss on travelling through the thickness of the panel and which because of incidence at certain points of the panel, emerge from said conical elements defining angles of between 60 and 90 with respect to the axis of symmetry of said conical elements strike an adjacent cone and suffer total internal reflection, thus reducing the low luminance of said panel. Said refracting elements of pyramidal form are situated on the exterior face of the panel forming therebetween narrow, flat zones whiclmprove the light efficiency of said panel without having an unfa vorable effect on the luminescence of said panel.

11 Claims, 10 Drawing Figures PATENTEI] FEBZB I974 SHEET 2 OF 5 PAT ENTE B FEB26I974 SHEET a 0F 5 PATENTEB FEB 2 61574 SHEET 5 [1F 5 NON-LUMINANCE LIGHTING PANEL CROSS REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION The invention refers to lighting panels for use in lighting units having fluorescent tubes as a lighting source, and more particularly refers to low luminescent lighting panels of the type described in my above mentioned patent which consists of an outer surface having a multiplicity of refracting prismatic elements in the form of cones or pyramids, the lateral surfaces of which are constructed such that luminous rays emerging from said cones or pyramids form angles of less than 60 with the axis of symmetry of said cones so'as to obtain a lighting panel of theoretically nil luminance.

In my patent, the laterally curved surface of the pyramids in an axial plane normal to two opposing laterally curved surfaces is bounded by two curved lines which are symmetric with respect to the axis of symmetry of the pyramid, each of which is made up an are which has its center situated on opposite sides of said axis of symmetry, and above the plane of the base of the pyramid. The cross section of the cones through an axial plane are defined by two lines symmetric with respect to the axis of symmetry of the cones, each one of which constitutes a first arc, the center of which is situated on the opposite side of said axis of symmetry and above the plane of the base of the cone, a straight line segment tangential to said first arc, and a second arc tengential to said straight line segment, the center of which is situated at the other side of said axis of symmetry of the cone and in the plane of the base of said cone.

In the panel of my patent the special structure of the refracting cones, in theory, causes all the rays which emerge from the cones to form angles of not more than 60 with respect to the axis of symmetry of the cones, the remaining rays undergo total internal reflection and are reflected towards the interior face of the panel, thus being eliminated and giving a panel of theoretically nil luminance. However, in practice, it has been found that some luminous rays with points of incidence at certain points on the interior surface of the panel may emerge from the exterior face of the panel forming angles of greater than t 5 with respect to the axis of symmetry of the cones. It has been discovered that these rays: which form an angle of between 60 and 90 with the axis of symmetry of the cones are particularly bright and therefore of primary concern with respect to the luminance of the panel where the rays strike the interior face of the panel in a direction which is normal or substantially normal to the surface of the panel, since such rays undergo little energy loss in their journey through the panel. On the other hand those luminous rays which strike the surface of the panel in directions substantially parallel to the interior surface, suffer a large energy loss on the journey through the panel by reflections in the surfaces of same, such that even if they do emerge from the opposite face of the panel in the above mentioned 60 to 90 zone they are quite weak and have little influence on the luminance of the panel. Thus, it is obvious that the light efficiency of the panel is in inverse ratio to the proportion of luminous rays capable of producing luminance which are eliminated by total internal reflection on their journey through the panel.

SUMMARY OF THE INVENTION Taking the foregoing into account the principal object of the invention is to provide an improved lighting panel of low luminance, having on its exterior surface a plurality of prismatic refracting elements in the form of cones having a curved lateral surface and rounded apex in which the luminance, caused by rays striking the panel at points on the interior face in a normal or substantially normal direction to said interior surface of the panel is eliminated.

Another object of the invention is to provide lighting panel of low luminance, having on its outer face refracting prismatic elements in the form of cones but having rounded apexes and including zones which do not influence the luminance of the panel and which increase the light efficiency of the panel.

A further object of the invention is to provide a panel of low luminance having on its exterior surface refracting prismatic elements in the form of pyramids having curved lateral faces and with an improved light output ratio.

Another object of the invention is to provide a lighting panel of low luminance having on its exterior surface refracting prismatic elements in the form of pyramids having curved lateral faces whereby the panel has improved mechanical rigidity.

Towards these objects, the invention comprises constructing the refracting cones of the panel such that the cones have circular bases and a peripheral surface defined by a line composed of a first arc and a second are having the centers situated on opposite sides of the axis of symmetry of the cone and above the plane of the base of said first and second arcs and a third are tangential to said straight line segments and having its center situated at the intersection of the axis of symmetry of the cone with the plane of the base of said cone.

The invention also comprises the positioning of the cones on the panel with the bases of each two adjacent cones superimposed on each other in such a way that the lateral surfaces of the cones intersect, thus reducing or eliminating flat portions of the panel between cones, reducing the luminance of the panel.

Another achievement of the invention refers to a panel with refracting prismatic elements in the form of pyramids having curved lateral surfaces as described in my patent and includes making these pyramids with squared bases and positioning them with their bases spaced in such a way that greater rigidity of the panel is achieved without an increase in weight, and at the same time increasing the light efficiency of the panel without unfavorably affecting the low luminance of the panel.

By thus positioning the refracting cones and pyramids, an improved light output ratio is obtained and at the same time if a ray should emerge from a prism or cone at an angle with respect to the axis of symmetry of the pyramid or cone of greater than it will strike the adjacent prism or cone and will consequently undergo total internal reflection, thus being eliminated.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a view in plan from below of a portion of a panel having refracting cones in staggered positions and tangential to one another and with some similar small cones between said cones. 7

FIG. 2 is a schematic cross-sectional view through the line IIII of FIG. 1 showing the path of the rays through the panel.

FIG. 3 is a view in plan from below of a panel having refracting cones in staggered positions and partially intersecting one another, two by two, the bases of the cones cut in hexaganal forms.

FIG. 4 is a schematic cross-sectional view through the line IV-IV of FIG. 3 showing the path of the luminous rays through the panel.

FIG. 5 is a view in plan from below of a portion of a panel having refracting cones positioned in rows along orthogonal lines and partially overlapping, two by two, the bases of said cones being cut in square form and having bevelled vertices and including similar small cones between the larger cones.

FIG. 6 is a schematic cross-sectional view through the line Vl-VI of FIG. 5 showing the path of the luminous rays through the panel.

FIG. 7 is a view in plan from below of a portion of a panel having refracting cones arranged in orthogonal rows and columns and partially overlapping one another and the bases of said cones being cut in square form.

FIG. 8 is a schematic cross-sectional view through the line VIIIVIII of FIG. 7 showing the path of luminous rays through the panel.

FIG. 9 is a view in plan from below of a portion of a panel having refracting pyramids of curved lateral surfaces and having square bases, arranged in orthogonal rows and columns and having their bases evenly spaced.

FIG. 10 is a schematic cross-sectional view through the line XX of FIG. 9 showing the path of the luminous rays through the panel.

DESCRIPTION OF PREFERRED EMBODIMENTS The primary purpose of this invention is to improve the lighting panel described in my US. Pat. No. 3,716,709 which refers to the profile of the axial section of the refracting cones and to the arrangement on the surface of the panel of said cones and of the refracting pyramids of curved lateral surfaces which consititute refracting prismatic elements of the panel of said patent.

The present invention comprises, in the case in which said prismatic refracting elements of the lighting panel are the aforementioned cones, constructing the cones according to the following description and positioning them appropriately. Referring to FIGS. 2, 4, 6 and 8 and curves 23 and 24, the surfaces of the cones are defined by two arcs which are, symmetric to the axis of symmetry of the cone and which have centers at the points 2 and 3 respectively situated on either side of said axis of symmetry on a line parallel to the plane of the base of said cone. Two line segments are situated above said plane, symmetric with respect to the axis of symmetry of the cone and tangential respectively to said two symmetric arcs. A third are is tangential to the two symmetric line segments and has its center at point 4 which is at the intersection of the plane of the base of the cone and the axis of symmetry thereof.

The cones constructed according to the form described can be arranged on the surface of the panel in the manner shown in FIG. 1 which corresponds with the arrangement FIG. 5 in my US. Pat. No. 3,716,709 according to which the cones are in staggered relation with their bases 9, ll, 13, tangential to each other, in pair-wise relationship and including some cones similar to those mentioned but of smaller dimension situated in the flat spaces 28 between the bases of three contiguous cones and with their respective bases 8, 10, 12 tangential to the bases of said larger cones.

In this layout and considering the line l-l' of the centers of the bases of the cones, the distance between the axis E and I, of two consecutive cones of bases 9 and 13 is equal to 2 E G ZG F tan 3.464 G F G F being the radius of the base of the cone.

Considering now FIG. 2 which is a cross section of the panel through the line II-ll of FIG. 1 which coincides with the line l-l' defined by the centers of the bases of the cones 9 and 13, we observe that the profile 23 of the surface of the cone 9 is constituted by a curved line comprising two arcs which are symmetric with respect to the axis E of the cone and have centers at the points 2 and 3 which are situated at either side of the axis E on a straight line parallel to said line 1-l' and above the plane of the interior face of the panel represented by the straight line ST the arcs extending from the plane of the exterior face of the panel to a line which preferable forms an angle of 45 with said straight line 2-3; an arc with its center at point 4 situated at the intersection of the axis E, of the cone and the plane of the exterior face of the panel and which extends preferably 45 beyond the axis E and two line segments symmetric with respect to said axis E and tangential to the are having center 4 and to the respective arcs having centers 2 and 3.

The profile 24 of the axial section of the cone of base 13 and of axis I is formed in the same manner as are the profiles of the remaining cones of the panel.

In FIG. 2 axial cross sections of the intermediate cones of small dimension of bases 10 and 12 the profiles of which, 25 and 26 are similar to the profiles 23 and 24 of the cones of bases 9 and 13 already described may be observed and it is seen that between these sections of cones 25 and 26 there is a flat portion indicated by the number 30.

Tracing the paths of various luminous rays which strike with different angles of incidence at points such as points 5, 6, and 7 on the interior face ST of the panel, it is seen that the luminous rays which strike the interior face ST of the panel in a direction normal to the face ST or nearly so, such as the rays d e f corresponding to point 5, undergo little energy loss as they travel through the thickness of the panel and are refracted by cone 23, emerging from it at an angle greater than 60 with respect to the axis E That is to say, the light rays emerge with an inclination and an intensity capable of producing luminance as a result of the form of the cusp of the cone, determined by the arc having its center at point 4. Such light rays however, undergo a deviation which results in their striking the following cone 24 in which they are refracted towards the interior face in the direction e 'f being thus eliminated,

while of the remaining rays a portion thereof undergoes total internal reflection, for example g ,h and some emerge at angles of less than 60 with the axis E thus producing no luminance. Only a very small portion of the rays emerge at an angle greater than 60 such as ray i, i, of point 7, but in this case they are rays which are incident on the interior face of the pane] ST, in directions nearly parallel to said plane ST and in their path through the panel undergo a large energy loss, and so emerge with low intensity, and as a practical matter do not cause any inconvenience.

In the embodiment represented in FIGS. 3 and 4, the refracting cones are staggered and partially intersect in such a way that the bases of said cones are cut in the form of regular hexagons, without having any flat surface between adjacent cones and the profiles 23, 24 of the axial sections of said cones are equal to that previously described in relation to the embodiment of FIGS. 1 and 2. As is shown in FIG. 3 since the radius of the base of said cones F H and the respective centers of the bases are situated on the straight line l4l4' the distance E 1 between the axis of symmetry of two consecutive nonadjacent cones of sections 23, 24, is determined by that is, it is equal to three times the radius of the circumference of the base of the cones.

The cross sectional view of FIG. 4 discloses that the path of the luminous rays corresponding to points 17 and 18 are analogous to those obtained by the embodiment of FIG. 2, while the luminous rays having points of incidence at G included between the bases of the cones 23 and 24 where the axial cross section presents the profile of the curve 27 corresponding to the line of intersection of the lateral surfaces of two adjacent cones, are refracted thus forming angles not greater than 39 with the between the base axis of symmetry E I which shows that luminence is not produced in this zone and that on the other hand an increase in the light output ratio from the panel as a whole is obtained.

In a third embodiment shown in FIGS. 5 and 6, the refracting cones are arranged in orthogonal rows and columns and have their lateral surfaces intersecting adjacent cones but leaving a small space between each set of four adjacent cones, in such a way that the bases of the said cones are cut in a square form having bevelled vertices, with small cones similar to those of 8, 10, 12, of FIG. 1 occupying those intermediate regions, with their bases tangential to the bases of said four adjacent cones, and in which the profile 25 ofa surface is similar to the profiles 23, 24 of the surfaces of the larger refracting cones.

The distance 5 between the axis of two consecutive cones, the centers of the bases of which are situated on the straight line -15 as are the centers of the bases of the corresponding small intermediate cones, is equal to 2 E l the diameter of the small intermediate cone; that is, about 2.31 times the value of the radius of the base of the cone.

In the present case, and as shown in FIG. 6 the length of the path of the luminous rays which have points of incidence at the points 19 and are also equal as in previous cases, while the rays having points of incidence at point 6:, coinciding with the axis of one of the small intermediate cones are refracted according to bundle of rays of concentrated form.

In another embodiment which is shown in FIGS. 7 and 8 the refracting cones are also arranged in orthogonal rows and columns with their adjacent lateral surfaces intersecting in such a way that their bases are in the form of squares which are contiguous to each other. That is they are arranged in an analogous form to that of FIG. 5 but without any intermediate spaces between the cones, and consequently there are no small dimension cones.

In this case the luminous rays with points of incidence at points 21 and 22 on the surface of the interior face of the panel, follow the same trajectories as those previously described, and as can be understood the same would occur with rays striking at point 6,.

Referring now to FIGS. 9 and 10, a low luminance lighting panel is shown having on its exterior surface a plurality of refracting prismatic elements consisting of pyramids each having a square base and having curved lateral surfaces, which more specifically are cylindrical surfaces. Its cross-section through an axial plane normal to two lateral opposite faces, represented by the line A B or by the line C D of FIG. 9, is bounded by two arcs F P and F P the centers of which are situated at points E and E respectively, which are symmetric with respect to the axis of symmetry of the pyramid and which are on a straight line parallel to the interior face of the panel and above it, similar to that described in my US. Pat. No. 3,716,709 with relation to FIG. 2 of the same.

According to the invention, in the embodiment of FIGS. 9 and 10, the surface of the exterior face of the panel does not coincide with the plane in which are situated the points F and F of intersection of the axial sections of the lateral faces of contiguous pyramids, but rather in a plane represented by the line G =,H,G ,H, situated at a distance 0 G in front of the mentioned plane, which is selected in such a manner that tangents such as HR, drawn from the points of intersection G ,H G ',H of the arcs which determine the axial cross section of each one of the pyramids to the arcs of the axial section of the continguous pyramide form angles of 60 with the direction normal to said plane of the exterior face of the panel.

With this layout I obtain an increase in the effective thickness of the panel and therefore of its mechanical rigidity in relation to the layout described in my above mentioned patent, there being some flat spaces of equal width formed between the continguous sides of the bases of the pyramids which are represented in the section of FIG. 10 by the elements of the straight line G H,.

and G H As shown in FIG. 10, the luminous rays a b c h i emanating from point M, of the interior surface of the panel follow a path similar to those represented in FlG.'8 of my patent. A portion of the luminous rays, j k L s t emenating from point N of the interior surface of the panel situated in front of one of the flat zones G H is refracted in a concentrated form according to the directions m 40 n 0, p and q which correspond exactly to those rays incident on the interior surface of the panel in a substantially normal direction to said surface, while the remaining rays undergo total internal reflection and are eliminated in the directions j k r s and r with the result that the flat spaces G H,

and G 'H considerably increases the light output ratio of the panel, without having an unfavorable influence on the low luminance of the panel.

If we consider a section of the panel through an axial plane which passes through one of the diagonals 1J or K1L1 of the base of the pyramid, similar results will be obtained. The only difference is that the arcs which define the axial section H P and G P would be replaced by eliptical arcs, due to dealing with the section of a cylinder through a plane oblique with respect to the generatrix of same.

As has been seen from the various possible embodiments of the invention, all provide reduction in the low luminance of the panel in relation to the embodiments described in my patent, or provide improvement of the light output ratio.

What I claim is:

l. A low-luminance lighting panel comprising a plurality of refracting prismatic elements of pointed dome shape situated on the outer surface of said panel, each of said elements having a circular base and an axis of symmetry wherein the lateral surfaces of said elements are defined by lines symmetric to said axis of symmetry of the pointed element, each of said lines being comprised of a first are having a center situated beyond the axis of symmetry of said pointed element and above the plane of the inner face of the panel, a line segment tangential to said first arc, and a second arc tangential to said line segment and having its center situated at the intersection of the axis of the symmetry of the element and the plane of the base of the element.

2. A lighting panel of low luminance comprising a plurality of main optical refracting elements of pointed dome shape situated on the outer surface of said panel,

each of said elements having a circular base and an axis of symmetry and having curved lateral surfaces with respect to the axis of symmetry of the pointed element, the cross-section of each of said main pointed elements taken through an axial plane being defined by a curved line comprising first and second arcs symmetric with respect to said axis of symmetry of the pointed element, each of said arcs having a center at a point situated beyond said axis of symmetry equidistant from said axis of symmetry and on a straight line parallel to the plane of the interior face of the panel, a third arc having its center situated at the intersection of the axis of symmetry of the pointed element with the base of said pointed element and covering equal angles on each side of said axis of symmetry of the pointed element, and two line segments symmetric with relation to said axis of symmetry of the pointed element and tangential respectively to said third are and to said first and second arcs of said elements defining flat regions between adjacent elements; and a plurality of optical refracting pointed elements of small dimension the axial cross section of which is similar to the axial cross section of said main pointed elements and situated in the flat spaces of the exterior face of the panel between the bases of said main pointed elements.

3. A lighting panel according to claim 2 wherein said main pointed elements are arranged in staggered relation on the outer face of the panel, having their bases tangential to others thereof and each of said smaller pointed elements having its base tangential to the bases of three surrounding main pointed elements.

4. A lighting panel, according to claim 2 wherein said main pointed elements are arranged on the exterior face of the panel in orthogonal rows and columns having their lateral surfaces intersecting others thereof such that the bases of said main pointed elements are in squared form having bevelled vertices according to an arc of the base of the pointed element, and each one of said similar but smaller pointed elements positioned between four main continguous pointed elements with its base tangential to the bases of the said four main pointed elements.

5. A low luminance lighting panel, having on its exterior surface a plurality of optical refracting elements of pointed dome shape having a circular base and an axis of symmetry wherein the axial cross sections of said pointed elements are defined by symmetric lines to said axis of symmetry of the pointed element each of said lines being composed ofa first are having its center situated beyond the axis of symmetry of the pointed element and above the plane of the inner face of the panel, a straight line segment tangential to said first and second arc, tangential to said straight line segment and having its center situated at the intersection of the axis of symmetry of the pointed element and the base of said pointed element, each of said refracting optical pointed elements partially intersecting other elements laterally.

6. A lighting panel, according to claim 5 wherein said refracting optical pointed elements are positioned in staggered relation on the outside face of the panel, in such a way that a common chord of the bases of each two intersecting pointed elements cover arcs of 60 of the circumferences of the bases, which have the form of regular hexagons.

7. A lighting panel according to claim 5 wherein the intersecting optical refracting pointed elements are arranged on the exterior face of the panel in orthogonal rows and columns.

8. A lighting panel according to claim 7, wherein the intersecting optical refracting pointed elements are arranged in such that the common chord of the bases of each two pointed elements defines arcs of of the circumference of these bases, which have square form.

9. A lighting panel according to claim 7 wherein the intersecting optical refracting pointed elements are arranged such that the common chord of the bases of each two intersecting pointed elements define arcs of less than 90 of the circumference of said bases, said bases thus having a squared form having bevelled vertices with small arcs and thus providing a flat space between each four continguous intersecting pointed elements, each flat space being occupied by a pointed element of smaller dimension, the axial section of which is similar to that of said refracting pointed elements, and having its base tangential to the bases of said four contiguous refracting intersecting pointed elements.

10. A low luminance lighting panel comprising a plurality of prismatic refracting elements on the outer surface of said panel, said elements being square based pyramids having lateral faces in the form of cylindrical surfaces, the axial cross section of said pyramids through a plane normal to two opposite lateral faces being defined by two arcs symmetric with respect to the axis of symmetry of the pyramid and the centers of which are situated at points beyond said axis of symmetry of the pyramid on a straight line parallel to the plane of the face of the interior surface of the panel and situated above it, said refracting pyramids being arranged on the outer face of the panel in orthogonal rows and columns, the sides of the bases of said continguous pyramids being evenly spaced from one another resulting in two orthogonal series of flat bands equally spaced.

the space between adjacent pyramids being defined such that a plane tangential to a lateral face of one of said two pyramids and containing the contiguous side of the base of the other pyramid forms an angle of 60 11. A lighting panel according to claim 10 wherein 5 with a plane normal to said exterior face of the panel.

the bases of two contiguous pyramids are separated, 

1. A low-luminance lighting panel comprising a plurality of refracting prismatic elements of pointed dome shape situated on the outer surface of said panel, each of said elements having a circular base and an axis of symmetry wherein the lateral surfaces of said elements are defined by lines symmetric to said axis of symmetry of the pointed element, each of said lines being comprised of a first arc having a center situated beyond the axis of symmetry of said pointed element and above the plane of the inner face of the panel, a line segment tangential to said first arc, and a second arc tangential to said line segment and having its center situated at the intersection of the axis of the symmetry of the element and the plane of the base of the element.
 2. A lighting panel of low luminance comprising a plurality of main optical refracting elements of pointed dome shape situated on the outer surface of said panel, each of said elements having a circular base and an axis of symmetry and having curved lateral surfaces with respect to the axis of symmetry of the pointed element, the cross-section of each of said main pointed elements taken through an axial plane being defined by a curved line comprising first and second arcs symmetric with respect to said axis of symmetry of the pointed element, each of said arcs having a center at a point situated beyond said axis of symmetry equidistant from said axis of symmetry and on a straight line parallel to the plane of the interior face of the panel, a third arc having its center situated at the intersection of the axis of symmetry of the pointed element with the base of said pointed element and covering equal angles on each side of said axis of symmetry of the pointed element, and two line segments symmetric with relation to said axis of symmetry of the pointed element and tangential respectively to said third arc and to said first and second arcs of said elements defining flat regions between adjacent elements; and a plurality of optical refracting pointed elements of small dimension the axial cross section of which is similar to the axial cross section of said main pointed elements and situated in the flat spaces of the exterior face of the panel between the bases of said main pointed elements.
 3. A lighting panel according to claim 2 wherein said main pointed elements are arranged in staggered relation on the outer face of the panel, having their bases tangential to others thereof and each of said smaller pointed elements having its base tangential to the bases of three surrounding main pointed elements.
 4. A lighting panel, according to claim 2 wherein said main pointed elements are arranged on the exterior face of the panel in orthogonal rows and columns having their lateral surfaces intersecting others thereof such that the bases of said main pointed elements are in squared form having bevelled vertices according to an arc of the base of the pointed element, and each one of said similar but smaller pointed elements positioned between four main continguous pointed elements with its base tangential to the bases of the said four main pointed elements.
 5. A low luminance lighting panel, having on its exterior surface a plurality of optical refracting elements of pointed dome shape having a circular base and an axis of symmetry wherein the axial cross sections of said pointed elements are defined by symmetric lines to said axis of symmetry of the pointed element each of said lines being composed of a first arc having its center situated beyond the axis of symmetry of the pointed element and above the plane of the inner face of the panel, a straight line segment tangential to said first and second arc, tangential to said straight line segment and having its center situated at the intersection of the axis of symmetry of the pointed element and the base of said pointed element, each of said refracting optical pointed elements partially intersecting other elements laterally.
 6. A lighting panel, according to claim 5 wherein said refracting optical pointed elements are positioned in staggered relation on the outside face of the panel, in such a way that a common chord of the bases of each two intersecting pointed elements cover arcs of 60* of the circumferences of the bases, which have the form of regular hexagons.
 7. A lighting panel according to claim 5 wherein the intersecting optical refracting pointed elements are arranged on the exterior face of the panel in orthogonal rows and columns.
 8. A lighting panel according to claim 7, wherein the intersecting optical refracting pointed elements are arranged in such that the common chord of the bases of each two pointed elements defines arcs of 90* of the circumference of these bases, which have square form.
 9. A lighting panel according to claim 7 wherein the intersecting optical refracting pointed elements are arranged such that the common chord of the bases of each two intersecting pointed elements define arcs of less than 90* of the circumference of said bases, said bases thus having a squared form having bevelled vertices with small arcs and thus providing a flat space between each four continguous intersecting pointed elements, each flat space being occupied by a pointed element of smaller dimension, the axial section of which is similar to that of said refracting pointed elements, and having its base tangential to the bases of said four contiguous refracting intersecting pointed elements.
 10. A low luminance lighting panel comprising a plurality of prismatic refracting elements on the outer surface of said panel, said elements being square based pyramids having lateral faces in the form of cylindrical surfaces, the axial cross section of said pyramids through a plane normal to two opposite lateral faces being defined by two arcs symmetric with respect to the axis of symmetry of the pyramid and the centers of which are situated at points beyond said axis of symmetry of the pyramid on a straight line parallel to the plane of the face of the interior surface of the panel and situated above it, said refracting pyramids being arranged on the outer face of the panel in orthogonal rows and columns, the sides of the bases of said continguous pyramids being evenly spaced from one another resulting in two orthogonal series of flat bands equally spaced.
 11. A lighting panel according to claim 10 wherein the bases of two contiguous pyramids are separated, the space between adjacent pyramids being defined such that a plane tangential to a lateral face of one of said two pyramids and containing the contiguous side of the base of the other pyramid forms an angle of 60* with a plane normal to said exterior face of the panel. 